Mems sensor with high voltage switch

ABSTRACT

A system and/or method for utilizing MEMS switching technology to operate MEMS sensors. As a non-limiting example, a MEMS switch may be utilized to control DC and/or AC bias applied to MEMS sensor structures. Also for example, one or more MEMS switches may be utilized to provide drive signals to MEMS sensors (e.g., to provide a drive signal to a MEMS gyroscope).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 14/723,927, filed on May 28, 2015, and entitled “MEMS SENSOR WITHHIGH VOLTAGE SWITCH”, which is incorporated herein by reference.

BACKGROUND

Various MEMS sensor architectures comprise sensor circuitry implementedin one or more integrated circuits. Such integrated circuits may, forexample, be implemented with CMOS technology. Particular types ofintegrated circuit technology may, however, be unable to effectivelyswitch signals at voltage levels that are desirable for efficient MEMSoperation.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a block diagram of an example MEMS sensor system, inaccordance with various aspects of the present disclosure.

FIG. 2A-2C show example block diagrams of out-of-plane MEMS switches, inaccordance with various aspects of the present disclosure.

FIGS. 3A-3B show example block diagrams of in-plane MEMS switches, inaccordance with various aspects of the present disclosure.

FIGS. 4A-4C show example block diagrams of compliant MEMS switches, inaccordance with various aspects of the present disclosure.

FIG. 5 shows an example block diagram of a MEMS sensor incorporatingMEMS switching for bias control, in accordance with various aspects ofthe present disclosure.

FIG. 6 shows an example block diagram of a MEMS sensor incorporatingMEMS switching for drive control, in accordance with various aspects ofthe present disclosure.

SUMMARY

Various aspects of this disclosure comprise a system and/or method forutilizing MEMS switching technology to operate MEMS sensors. As anon-limiting example, a MEMS switch may be utilized to control DC and/orAC bias applied to MEMS sensor structures. Also for example, one or moreMEMS switches may be utilized to provide drive signals to MEMS sensors(e.g., to provide a drive signal to a MEMS gyroscope).

DETAILED DESCRIPTION OF VARIOUS ASPECTS OF THE DISCLOSURE

The following discussion presents various aspects of the presentdisclosure by providing various examples thereof. Such examples arenon-limiting, and thus the scope of various aspects of the presentdisclosure should not necessarily be limited by any particularcharacteristics of the provided examples. In the following discussion,the phrases “for example,” “e.g.,” and “exemplary” are non-limiting andare generally synonymous with “by way of example and not limitation,”“for example and not limitation,” and the like.

The following discussion may at times utilize the phrase “A and/or B.”Such phrase should be understood to mean just A, or just B, or both Aand B. Similarly, the phrase “A, B, and/or C” should be understood tomean just A, just B, just C, A and B, A and C, B and C, or all of A andB and C.

The following discussion may at times utilize the phrases “operable to,”“operates to,” and the like in discussing functionality performed byparticular hardware, including hardware operating in accordance withsoftware instructions. The phrases “operates to,” “is operable to,” andthe like include “operates when enabled to.” For example, a module thatoperates to perform a particular operation, but only after receiving asignal to enable such operation, is included by the phrases “operatesto,” “is operable to,” and the like. Also for example, circuitry is“operable” to perform a function whenever the circuitry comprises thenecessary hardware and code (if any is necessary) to perform thefunction, regardless of whether performance of the function is disabled,or not enabled (e.g., by a user-configurable setting, factory trim,etc.).

The following discussion may at times refer to various system or devicefunctional modules or circuitry (e.g., sensor processing circuitry,proof mass drive control circuitry, etc.). It should be understood thatthe functional modules or circuitry were selected for illustrativeclarity and not necessarily for providing distinctly separate hardwareand/or software modules. For example, any one or more of the modules orcircuits discussed herein may be implemented by shared hardware,including for example a shared processor. Also for example, any one ormore of the modules discussed herein may share software portions,including for example subroutines. Additionally for example, any one ormore of the modules discussed herein may be implemented with independentdedicated hardware and/or software. Accordingly, the scope of variousaspects of this disclosure should not be limited by arbitrary boundariesbetween modules and/or circuits unless explicitly claimed. Additionally,it should be understood that when the discussion herein refers to amodule or circuit performing a function, the discussion is generallyreferring to either a pure hardware module implementation and/or aprocessor operating in accordance with software. Such software may, forexample, be stored on a non-transitory machine-readable medium.

In various example implementations discussed herein, a chip is definedto include at least one substrate typically formed from a semiconductormaterial. A single chip may for example be formed from multiplesubstrates, where the substrates are mechanically bonded to preserve thefunctionality. Multiple chip (or multi-chip) includes at least 2substrates, wherein the 2 substrates are electrically connected, but donot require mechanical bonding.

A package provides electrical connection between the bond pads on thechip (or for example a multi-chip module) and a metal lead that can besoldered to a printed circuit board (or PCB). A package typicallycomprises a substrate and a cover. An Integrated Circuit (IC) substratemay refer to a silicon substrate with electrical circuits, typicallyCMOS circuits. A MEMS substrate provides mechanical support for the MEMSstructure(s). The MEMS structural layer is attached to the MEMSsubstrate. The MEMS substrate is also referred to as handle substrate orhandle wafer. In some embodiments, the handle substrate serves as a capto the MEMS structure.

In the described examples, an electronic device incorporating a sensor(e.g., one or more of the sensors discussed herein) may, for example,employ a motion tracking module also referred to as Motion ProcessingUnit (MPU) that includes at least one sensor in addition to electroniccircuits. The at least one sensor may comprise any one or more of avariety of sensors, such as for example a gyroscope, a compass, amagnetometer, an accelerometer, a microphone, a pressure sensor orbarometer, a resonator, a mass sensor, a chemical sensor, a proximitysensor, a moisture sensor, a temperature sensor, a biometric sensor, oran ambient light sensor, among others known in the art.

Some example system implementations may, for example, comprise anaccelerometer, gyroscope, and magnetometer or other compass technology,which each provide a measurement along three axes that are orthogonalrelative to each other, and may be referred to as 9-axis devices. Otherexample system implementations may, for example, comprise anaccelerometer, gyroscope, compass, and pressure sensor, and may bereferred to as 10-axis devices. Other embodiments might not include allthe sensors or may provide measurements along one or more axes.

The various sensors discussed herein may, for example, be formed on afirst substrate. Various embodiments may, for example, includesolid-state sensors and/or any other type of sensors. The electroniccircuits in the MPU may, for example, receive measurement outputs fromthe one or more sensors. In various example implementations, theelectronic circuits process the sensor data. The electronic circuitsmay, for example, be implemented on a second silicon substrate. In someexample implementations, the first substrate may be vertically stacked,attached and electrically connected to the second substrate in a singlesemiconductor chip, while in other example implementations, the firstsubstrate may be disposed laterally and electrically connected to thesecond substrate in a single semiconductor package (e.g., both attachedto a common packaging substrate or other material). In other exampleimplementations, the sensors may, for example, be formed on differentrespective substrates (e.g., all attached to a common packagingsubstrate or other material).

In an example implementation, the first substrate is attached to thesecond substrate through wafer bonding, as described in commonly ownedU.S. Pat. No. 7,104,129, which is hereby incorporated herein byreference in its entirety, to simultaneously provide electricalconnections and hermetically seal the MEMS devices. This fabricationtechnique advantageously enables technology that allows for the designand manufacture of high performance, multi-axis, inertial sensors in avery small and economical package. Integration at the wafer-levelminimizes parasitic capacitances, allowing for improved signal-to-noiserelative to a discrete solution. Such integration at the wafer-levelalso enables the incorporation of a rich feature set which minimizes theneed for external amplification.

Reducing the fabrication cost of MEMS devices is generally related tothe material footprint, and one example way to reduce size and thereforecost of MEMS is by using smaller (e.g., nanometer “nm”) CMOS technology.180 nm, 40 nm and 18 nm are examples of nm CMOS technology. The nmnumber describes the smallest feature and therefore a circuit on 18 nmCMOS will fit in a smaller foot print than the same circuit on 180 nmCMOS. However, transistors on relatively smaller nm CMOS have a lowerbreak down voltage than on relatively larger nm CMOS, and thereforecannot switch the same voltage magnitude as the larger nm CMOScounterpart. Voltage magnitude for DC and AC signals affects MEMS sensorsensitivity, and voltage duty cycling affects MEMS power consumption andnoise. Therefore a problem may arise using low nm CMOS to reduce cost,as it also lowers the switching voltage magnitude, which degrades theMEMS sensor performance. Various aspects of this disclosure provide forlower cost by using low nm CMOS without reducing MEMS sensorperformance, for example by utilizing a MEMS high voltage switch insteadof the low nm CMOS transistor switch.

Commercial switches are large and discrete devices. Such switches aredesigned for relatively high current and thus commonly made from metal.The MEMS switches in accordance with various aspects of this disclosure,however, are significantly smaller than commercially available switchesand/or are made with a same MEMS process as that of the MEMS sensorsdiscussed herein. Since electrical current levels in accordance withvarious aspects of this disclosure may be relatively small (e.g., lessthan 1 milliamp, less than 100 microamps, etc.), the MEMS switches maybe substantially smaller than those commercially available.

The general focus of current MEMS switch research is on relatively highswitching frequencies (e.g., above 1 MHz, above 1 GHz, etc.) andmaintaining a long device life under operation at such high switchingfrequencies. The MEMS switches in accordance with various aspects ofthis disclosure, however, may switch in the KHz range (e.g., less than30 KHz, less than 100 KHz, etc.), and thus lifetime issues are ofsignificantly less concern than with their high-frequency counterparts.

Accordingly, in accordance with various aspects of this disclosure, anew MEMS switch is proposed, for example in conjunction with a low-nmCMOS. The new MEMS switch, for example, may be specifically designed forthe needs (e.g., electrical current magnitude, switching frequency,etc.) of MEMS sensors interfacing with low-nm CMOS.

MEMS sensors are biased at a DC voltage and some sensors are driven withan AC voltage. Both the DC voltage bias and the AC voltage signals mayimpact the sensitivity of the sensor and it may therefore be beneficialto use a high DC bias voltage and a high AC voltage. Switching may also,for example, affect other sensor performance parameters (e.g.,self-test, power, and noise). Sensors may, for example, be turned on,off, or duty cycled to control power consumption allowing for low powerand/or low noise sensor operation. To achieve these states ofperformance there may, for example, be a need to switch high voltagesignals. Charge pumps in CMOS circuits may, for example, be used toincrease the voltage magnitude and can generally be implemented in lownm CMOS technology. However, once the high voltage is generated, the lownm CMOS technology transistors cannot effectively switch the highvoltage signals, for example because of the lower voltage breakdownassociated with low nm CMOS technology.

Accordingly, various aspects of the present disclosure provide a systemand/or method for utilizing MEMS switching technology (e.g., mechanicalswitching technology) to operate MEMS sensors, for example in MEMSsensor architectures in which underlying semiconductor circuitry isincapable of effectively performing the desired switching. In accordancewith various aspects of the present disclosure any of a variety of MEMSswitch structures may be utilized, non-limiting examples of which willbe discussed herein.

FIG. 1 shows a block diagram of an example MEMS sensor system 100, inaccordance with various aspects of the present disclosure. The system100 (e.g., implemented on a single chip, in a single package, in amulti-package circuit, etc.) may, for example, comprise CMOS circuitryand MEMS switches.

The example system 100 comprises an integrated circuit (e.g., a silicondie) 110. A portion of the example integrated circuit 110 implements atleast one chart pump 115. Though the example system 100 only shows onecharge pump 115, it should be understood that a plurality of chargepumps may be implemented.

The example system 100 also comprises a plurality of MEMS switches 122,124, 126, and 128, each of which receiving a respective signal from thecharge pump 115. The first MEMS switch 122, for example, receives a highvoltage signal (e.g., a 25V signal, a signal at a voltage above 20V, asignal at a voltage above 15V, etc.). For example, the first MEMS switch122 may receive a first signal 116 from the charge pump 115 at a firstvoltage level (e.g., that the CMOS technology utilized to implement theintegrated circuit 110 is not capable of effectively switching). Suchfirst voltage level may, for example, be at or above the breakdownvoltage of a transistor of the integrated circuit 110. The first MEMSswitch 122, for example, is utilized to switch on and off a DC biassignal 123 to a first MEMS sensor 132 (e.g., for example a gyroscope, acompass, a magnetometer, an accelerometer, a microphone, a pressuresensor, a proximity sensor, a moisture sensor, a temperature sensor, abiometric sensor, or an ambient light sensor, etc.).

The second MEMS switch 124, or for example a plurality of MEMS switches,receives a second signal 117 from the charge pump 115 at a secondvoltage level (e.g., that the CMOS technology utilized to implement theintegrated circuit 110 is not capable of effectively switching, notcapable of switching effectively at a desired switching rate, etc.).Such second voltage level may, for example, be the same as the firstvoltage level. Such second voltage level may, for example, be at orabove the breakdown voltage of a transistor of the integrated circuit110. The second MEMS switch 124, for example, is utilized to switch anAC drive signal 125 to the first MEMS sensor 132.

The third MEMS switch 126, or for example a plurality of MEMS switches,receives a third signal 118 from the charge pump 115 at a third voltagelevel (e.g., that the CMOS technology utilized to implement theintegrated circuit 110 is not capable of effectively switching, notcapable of switching effectively at a desired switching rate, etc.).Such third voltage level may, for example, be the same as the firstand/or second voltage level. Such third voltage level may, for example,be at or above the breakdown voltage of a transistor of the integratedcircuit 110. The third MEMS switch 126, for example, is utilized toswitch an AC drive signal 127 to a second MEMS sensor 134 (e.g., forexample a gyroscope, a compass, a magnetometer, an accelerometer, amicrophone, a pressure sensor, a proximity sensor, a moisture sensor, atemperature sensor, a biometric sensor, or an ambient light sensor,etc.).

The fourth MEMS switch 128, or for example a plurality of MEMS switches,receives a fourth signal 119 from the charge pump 115 at a fourthvoltage level (e.g., that the CMOS technology utilized to implement theintegrated circuit 110 is not capable of effectively switching, notcapable of switching effectively at a desired switching rate, etc.).Such fourth voltage level may, for example, be the same as the firstvoltage level, second voltage level and/or third voltage level. Suchfourth voltage level may, for example, be at or above the breakdownvoltage of a transistor of the integrated circuit 110. The fourth MEMSswitch 128, for example, is utilized to switch one or more self-testsignals 129 (e.g., one or more DC and/or AC signals) to the second MEMSsensor 134.

The example system 100 is also shown providing a fifth signal 131, forexample at a fifth voltage level to the second MEMS sensor 134. Thefifth signal 129 may, for example, be a low voltage signal (e.g., at afifth voltage level, for example 5V, 4V, 2.5V or less, etc.) to thesecond MEMS sensor 134. Such a fifth voltage level may, for example, belower than the first voltage level, second voltage level, third voltagelevel and/or fourth voltage level. Such a fifth voltage level may, forexample, be below the breakdown voltage of a transistor of theintegrated circuit 110.

Though not illustrated in FIG. 1 for the sake of clarity, the switchingof the MEMS switches 122, 124, 126, and 128 may be controlled by controlcircuitry of the integrated circuit 110. For example, the integratedcircuit 110 may operate to determine when to actuate the MEMS switchesand then output one or more signals to cause such actuation.

The configuration of the MEMS switches 122, 124, 126 and 128 maycomprise any of a variety of characteristics, non-limiting examples ofwhich are presented herein (e.g., in FIGS. 2-6).

FIGS. 2A-2C show example block diagrams of out-of-plane MEMS switches,in accordance with various aspects of the present disclosure. Any of theMEMS switches 200, 250 and 280 shown in FIGS. 2A-2C may share any or allcharacteristics with each other.

Referring to FIG. 2A, the example MEMS switch 200 comprises anintegrated circuit (IC) layer 205, for example a CMOS layer. The switch200 also comprises a MEMS post anchor 210, which couples the MEMS switchlever 215 to the IC layer 205. The switch 200 also comprises an actuatorelectrode 220 and a contact electrode 225.

In operation, a switch control signal applied to the actuator electrode220 drives the MEMS switch lever 215 (or arm, or flexible arm) to touchthe contact electrode 225, and removal of the switch control signalallows the MEMS switch lever 215 to return to its steady state positionthat is out of touch with the contact electrode 225. As shown in FIGS.2B and 2C, the contact electrode 225 and/or the actuator electrode 220may, for example, be made from various materials, for example comprisingone or more of: a semiconductor material such as silicon (e.g., dopedsilicon, a metal, titanium nitride (TiN), etc.).

Though not shown in some of the figures, the post anchor 210 may beconnected to an electrical terminal and provide a conductive pathbetween the electrical terminal and the MEMS switch lever 215. The postanchor 210 and MEMS switch lever 215 may then be energized, and transfersuch energy to the contact electrode 225 when the MEMS switch lever 215is actuated to touch the contact electrode 225.

In an example scenario, the MEMS switch lever 215 (or arm) may beenergized at 25V, so that the contact electrode 225 would be energizedat 25V or 0V, depending on whether the MEMS switch lever 215 is touchingthe contact electrode 225 or not, respectively.

The actuator electrode 220 may, for example, comprise an electrostaticactuator (e.g., a low-voltage actuator controlled by a CMOS transistor,for example of the IC 110 of FIG. 1) that applies an attractive force tothe MEMS switch lever 215 when it is desired to pull the MEMS switchlever 215 into contact with the contact electrode 225. The controlsignal applied to the actuator electrode 220 may, for example, comprisea voltage that does not exceed the break down voltage of the controllingcircuitry (e.g., CMOS transistors of the integrated circuit 110). Forexample, the control signal applied to the actuator electrode 220 may bea 5V signal, a signal at or below 2.5V, etc.

It should be noted that although a normally open configuration isillustrated for the MEMS switch 200, a normally closed configuration mayalso be used.

The portion of the MEMS switch lever 215 that contacts the contactelectrode 225, and the contact electrode 225, may be shaped and sized toconduct enough charge for the particular application. For example, thesize and/or shape of respective mating surfaces on the contact electrode225 and the MEMS switch lever 215 may be selected. Additionally, themating surfaces may be smoothed and/or coated to enhance conductivitybetween the contacting surfaces when mated. The MEMS material used forMEMS components of the switch 200 may be selectively chosen to providethe desired conductivity. For example, a low-doped MEMS material atabout 0.02 ohms/cm or a highly-doped MEMS material at about 0.005ohms/cm may be selected (e.g., for one or more mating surfaces, forexample the contact electrode, MEMS switch lever 215, etc.). Othercoatings may, for example, be applied to surfaces (e.g., matingsurfaces) to improve performance. An example of this is the applicationof Self-Assembled Monolayers (SAM) to prevent sticking/welding aftercontact called stiction. Note that although the MEMS switch lever 215(or arm) is shown implemented in a MEMS layer, a MEMS switch lever mayalso be formed in a CMOS layer.

Turning now to FIG. 2B, the MEMS switch 250 is shown in a configurationin which the MEMS switch lever 265 (or arm), the post anchor 260, theactuator electrode 270, and the contact electrode 275 are all formedfrom semiconductor material (e.g., silicon).

The post anchor 260, actuator electrode 270, and contact electrode 275are formed on an oxide layer 255. Though not illustrated, below theoxide layer 255 may be a silicon layer, for example forming asilicon-oxide-silicon layered topology. In such a configuration, forexample, there might not be any semiconductor circuitry (e.g., activedevices) formed in the silicon. For example, semiconductor circuitry maybe coupled to the MEMS switch components by wire bonding.

In this example configuration, the MEMS switch lever 265 contacts thecontact electrode 270 in a silicon-to-silicon contact. Unless coatedwith a smooth material, the contact area is generally rough.Accordingly, the size and shape of the contact electrode 270 and theportion of the MEMS switch arm 265 that contacts the contact electrode270 should be selected to provide at least the minimum desiredconductance.

Turning now to FIG. 2C, the MEMS switch 280 is shown in an exampleconfiguration in which the MEMS material is coupled to the IC 285 (e.g.,CMOS) circuitry, for example utilizing a eutectic bond (e.g., analuminum-germanium eutectic bond). In the example configuration, theMEMS switch 280 may comprise a post anchor 290 and MEMS switch lever 295made from silicon, an actuator electrode 297 and contact electrode 298made from metal, and an aluminum-germanium eutectic bond 287 and 288between the post anchor 290 and the IC 285 (e.g., CMOS) layer. In theMEMS switch 280, the MEMS switch lever 295 (or arm) contacts the metalcontact electrode 298 when actuated. The point of contact is thus asilicon-to-metal contact. As opposed to the silicon-to-silicon contactdiscussed herein with regard to FIG. 2B, the example silicon-to-metalcontact may provide a better conductive interface. For example, thecontact electrode 298 metal (e.g., aluminum, copper, gold, etc.) mayconform to the hardened silicon surface of the MEMS switch lever 295over time and impacts. Though not illustrated, the MEMS switch 280 mayalso comprise an oxide on the IC 285 (e.g., CMOS) layer, for example,between the IC 285 and the metal members and/or between the metalmembers.

Though the example MEMS switch 280 illustrated in FIG. 2C comprises analuminum-germanium eutectic bond, any of a variety of bondingtechnologies may be utilized.

FIGS. 2A-2C presented example block diagrams of example out-of-planeMEMS switches, in accordance with various aspects of the presentdisclosure. Other example configurations that may be utilized comprisein-plane switch configurations, examples of which will now be provided.

FIGS. 3A-3B show example block diagrams of in-plane MEMS switches, inaccordance with various aspects of the present disclosure. Such figuresshow top-down views of respective in-plane MEMS switches. Though FIGS.3A-3B show a configuration like FIG. 2C, in which the MEMS componentsare stacked on a CMOS layer, the scope of various aspects of thisdisclosure should not be limited to such structure. For example, theexample in-plane switches of FIGS. 3A-3B may share any or all structuralcomponents with the MEMS switches 200, 250, and 280 illustrated in FIGS.2A-2C and discussed herein.

Referring to FIG. 3A, the example MEMS switch 300 comprises a first postanchor 310 coupled to the IC layer 305 (e.g., CMOS layer) to which theMEMS switch lever 315 (or arm) is coupled. The MEMS switch 300 alsocomprises a second post anchor 322 to which the actuator 320 is coupled,and a third post anchor 327 to which the contact 325 is coupled. TheMEMS switch 300 may, for example, may operate in a manner generallyanalogous to that discussed with regard to the MEMS switches 200, 250and 280 of FIGS. 2A-2C, albeit with a different plane of motion for theswitch lever 315.

The MEMS switch 300 is shown in a single-pole single-throw configuration(as with FIGS. 2A-2C), but the scope of various aspects of thisdisclosure is not so limited. For example, as shown in FIG. 3B, the MEMSswitch 350 may be formed in a single-pole double-throw configuration.For example, the MEMS switch 350 may comprise any or all of thecomponents of the MEMS switch 300. The MEMS switch 350 may also comprisea third post anchor 372, coupled to the IC layer 305, to which a secondactuator 370 is coupled. The MEMS switch 350 may further comprise afourth post anchor 377 to which a second contact 375 is coupled.

Additionally, though not shown, the MEMS switches discussed herein maybe formed in any of a variety of other configurations depending onoverall system needs (e.g., double-pole single-throw, double-poledouble-throw, etc.).

As with FIGS. 2A-2C, the actuator (320 and/or 370) and/or contact (325and/or 375) may be formed, for example, of semiconductor material ormetal. Also for example, the bonding technique utilized between the MEMSmaterial and the underlying semiconductor material (e.g., comprisingCMOS circuitry, semiconductor material with no active electrical devicesformed therein, etc.) may comprise eutectic bonding as discussed herein,or another technique.

The MEMS switches, examples of which are illustrated in FIGS. 2A-2C and3A-3B may, for example, comprise relatively rigid (or stiff) components.In such a configuration, the structural soundness of the materials(e.g., silicon, metal, etc.) at the point of impact between the MEMSswitch lever and the contact may directly affect the life of the switch.Compliance may be incorporated into the MEMS switch to reduce theeffects of the lever/contact collision and thus increase the reliabilityand/or longevity of the switch. The compliance may, for example, beimplemented mechanical structures (e.g., MEMS structures), coatings,etc. Non-limiting examples of compliance structures are illustrated inFIGS. 4A-4C.

FIGS. 4A-4C show example block diagrams of compliant MEMS switches, inaccordance with various aspects of the present disclosure. The MEMSswitches 400, 450, and 480 may, for example, share any or allcharacteristics with the example MEMS switches illustrated in FIGS.2A-2C and 3A-3B and discussed herein and/or any MEMS switches discussedherein.

The MEMS switch 400 shown in FIG. 4A may, for example, comprise a springstructure 407 incorporated into (e.g., formed integrally with) orattached to the MEMS switch lever 415 (or arm) at the point of contactto add structural compliance at the point of impact between the MEMSswitch lever 415 and the contact 425. For example, the spring structure407 may comprise a protrusion 408 to contact the contact 425, where theprotrusion 408 is coupled to a flex portion 409 having springcompliance. The example spring structure 407 comprises a cavity 406 intowhich the flex portion 409 may flex when the protrusion 408 impacts thecontact 425. The spring structure 407 may comprise characteristics ofany of a variety of MEMS spring structures, for example, leaf springs,folded springs, lever arm springs, etc. The spring structure 407 may beformed in any of a variety of manners. For example, the spring structure407 may be formed in the MEMS material (e.g., silicon) of the MEMSswitch lever 415.

Also, the MEMS switch 450 shown in FIG. 4B may, for example, comprise aspring structure 457 incorporated into (e.g., formed integrally with) orattached to the contact 475 at the point of contact between the MEMSswitch lever 465 and the contact 475 to add structural compliance at thepoint of impact between the MEMS switch lever 465 and the contact 475.For example, the spring structure 457 may comprise a protrusion 458 tocontact the MEMS switch lever 465, where the protrusion 458 is coupledto a flex portion 459 having spring compliance. The example springstructure 457 comprises a cavity 456 into which the flex portion 459 mayflex when the protrusion 458 impacts the MEMS switch lever 465. Thespring structure 457 may comprise characteristics of any of a variety ofMEMS spring structures, for example, leaf springs, folded springs, leverarm springs, etc. The spring structure 457 may be formed in any of avariety of manners. For example, the spring structure may be formed inthe MEMS material (e.g., silicon) of the contact 475. Also for example,the spring structure 457 may be formed in the metal of a metal contact.

Additionally, the MEMS switch 480 shown in FIG. 4C may, for example,comprise both of the spring structures 407 and 457 shown in FIGS. 4A and4B.

In addition to, or instead of, spring structures being built into theMEMS switch structure, various surface artifacts may also beincorporated into the surface of the MEMS material and/or contactmaterial to increase the longevity of the MEMS switch. For example,scallops may be formed to enhance the reliability of the MEMS switchstructure.

Also, in addition to, or instead of, compliant structures being builtinto the MEMS switch structure, various coatings may be utilized at thepoint of contact between the MEMS switch lever (or arm) and the contactto enhance the performance of the contact. Such coatings may, forexample, provide compliance at the point of contact between the MEMSlever arm and the contact. For example, as discussed herein, aSelf-Assembled Monolayer (SAM) may be applied, for example to preventstiction. Such a SAM may also beneficially add compliance at the pointof contact. Additionally, such coatings may be utilized to enhanceconductivity, protect contacting surfaces from wear, etc.

As discussed herein, MEMS switching may be utilized to control biasvoltages and/or drive signals for MEMS sensors. Further non-limitingexamples of such utilization will now be provided.

Turning next to FIG. 5, such figure shows an example block diagram of aMEMS sensor 500 incorporating MEMS switching for bias control, inaccordance with various aspects of the present disclosure. The biasbeing controlled by the MEMS switch 505 may, for example, be at avoltage and/or frequency that the underlying semiconductor circuittechnology is unable to provide. For example, the voltage level may beat a level beyond the breakdown voltage of electrical circuitry (e.g.,CMOS circuitry) controlling the MEMS switch 505. The MEMS sensor 500may, for example, comprise an accelerometer sensor, but the scope ofvarious aspects of this disclosure is not limited to accelerometersensors.

The MEMS switch 505 may, for example, be utilized to apply a bias 507(e.g., a DC and/or AC bias) to the proof mass M and/or stationaryportions of the MEMS sensor 500. Such a bias may, for example, beprovided continually, as needed, periodically, etc. For example, theMEMS switch 505 may be activated to apply a bias 507 to the MEMSstructural element(s) at sample times. For example, in an examplescenario in which a sensor sample rate is 100 Hz, the MEMS switch 505may be utilized to apply the bias 507 for each sample (e.g., in time forthe bias 507 to reach steady state before the sample is taken) and thenremoved 100 times per second.

Also for example, the MEMS switch 505 may be utilized to apply the bias507 during periods of use for particular MEMS sensors. For example, in asensor circuit architecture comprising a plurality of sensors, therespective bias for each sensor may be separately controlled.Alternatively, in a scenario in which the plurality of sensors share aMEMS bias switch, a single bias may be applied to the plurality ofsensors when any of the sensors are to be biased.

Additionally, the MEMS switch 505 may be utilized to provide an AC biasto the various MEMS structures. For example, the MEMS switch 505 may beoperated to provide a square wave bias to the various MEMS structures asneeded, for example to the proof mass M, to stationary components (e.g.,sidewalls) of the MEMS sensor 500, etc.

Though the sensor circuit 500 of FIG. 5 is described generally herein interms of an accelerometer, the scope of various aspects of thisdisclosure is not limited thereto. For example, the sensor circuit maycomprise a MEMS magnetometer, barometer, etc. Also for example, thesensor may comprise various portion of a MEMS gyroscope that may bebiased.

As discussed herein, in addition to or instead of bias control, MEMSswitches may be utilized to generate drive signals for driven MEMSsensor devices (e.g., MEMS gyroscope devices and/or other sensors withdriven components). A non-limiting example of a MEMS gyroscope sensorcircuit 600 that utilizes MEMS switching in accordance with variousaspects of this disclosure is shown at FIG. 6. The circuit 600 and/orthe components thereof may, for example, share any or allcharacteristics with the other example systems, circuits, and/or MEMSsensors discussed herein.

The sensor circuit 600 comprises a mass 610, which may also be referredto herein as a proof mass, which is driven in a vibratory or oscillatorymanner in the drive direction, labelled “D” in FIG. 6. The drivecircuitry may, for example, comprise a drive sensor 615 (e.g., acapacitive sensor or other type of sensor), a drive sense amplifier 620,a phase detector 625, a MEMS switch drive module 630, and a driveelement 645 (e.g., an electrostatic drive element). The drive sensor 615may, for example, sense movement of the proof mass 610 in the drivedirection “D” and output a drive sense signal indicative of the senseddrive motion of the proof mass 610. The drive sense amplifier 620 maythen amplify the drive sense signal provided by the drive sensor 615,and provide the amplified drive sense signal to the phase detector 625and the MEMS switch drive module 630. The phase detector 625 outputs anin-phase signal “I” (which is in phase with the drive signal) to theMEMS switch drive module 630 to utilize in synchronizing the switchingof the MEMS drive switch(es) in the drive module 630. The drive signalis then provided to the drive element 645, which generates the force(e.g., electrostatic force) to vibrate the proof mass 610. The MEMSswitch drive module 630 may, for example, comprise one or more MEMSswitches (e.g., any of the MEMS switches discussed herein) arranged inan inverter configuration to provide an AC drive voltage to the driveelement 645.

The circuit 600 may also, for example, comprise a Coriolis sensor 650, aCoriolis sense amplifier 655, a sense mixer 660, and a low-pass filter665. The Coriolis sensor 650 may, for example, sense movement of theproof mass 610 in the sense direction “S” and output a Coriolis sensesignal indicative of the sensed motion of the proof mass 610. The signaloutput from the Coriolis sensor 650 will generally, for example,comprise a composite signal that includes a signal indicative of theCoriolis force caused by rotation of the gyroscope and also a quadraturesignal. The Coriolis sense amplifier 655 may then amplify the Coriolissense signal provided by the Coriolis sensor 650, and provide theamplified Coriolis sense signal to the sense mixer 660. The sense mixer660 also receives the in-phase signal output by the phase detector 625.The sense mixer 660 mixes the in-phase signal and the amplified Coriolissense signal to generate a signal with the quadrature componentsremoved. The output of the sense mixer 660 is then filtered by low-passfilter (LPF) 665 and output as a signal Omega, which is indicative ofthe angular velocity at which the gyroscope is being rotated.

Other examples of gyroscope structures and/or circuitry may, forexample, be found in commonly owned U.S. Pat. No. 8,833,162, titled“Micromachined Gyroscope Including a Guided Mass System,” filed Sep. 16,2011; and U.S. patent application Ser. No. 14/041,810, titled“Micromachined Gyroscope Including a Guided Mass System,” filed Sep. 30,2013, each of which are hereby incorporated herein by reference in itsentirety.

The present disclosure provides various MEMS switch characteristics andvarious MEMS sensor implementations utilizing MEMS switches, for examplefor bias and/or drive control. The scope of this disclosure should notbe limited to the particular MEMS switch and/or sensor implementationexamples provided herein.

As discussed herein, any one or more of the functions (e.g., MEMSswitching control functions, charge pump functions, sensor processingfunctions, etc.) may be implemented by a pure hardware design and/or bya processor (e.g., an application or host processor, a sensor processor,etc.) executing software instructions. Similarly, other examples maycomprise or provide a non-transitory computer readable medium and/orstorage medium, and/or a non-transitory machine readable medium and/orstorage medium, having stored thereon, a machine code and/or a computerprogram having at least one code section executable by a machine and/ora computer (or processor), thereby causing the machine and/or computerto perform the functions as described herein.

In summary, various aspects of the present disclosure provide a systemand/or method for utilizing MEMS switching technology to operate MEMSsensors (e.g., MEMS sensors having resonant MEMS structures, for examplevarious implementations of gyroscopes, magnetometers, accelerometers,etc.). While the foregoing has been described with reference to certainaspects and embodiments, it will be understood by those skilled in theart that various changes may be made and equivalents may be substitutedwithout departing from the scope of the disclosure. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the disclosure without departing from its scope.Therefore, it is intended that the disclosure not be limited to theparticular embodiment(s) disclosed, but that the disclosure will includeall embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A MEMS device comprising: a MEMS switch operableto switch a signal, wherein the MEMS switch comprises: a post anchor; aflexible MEMS arm coupled to the post anchor; an actuator electrode; anda contact electrode.
 2. The MEMS device of claim 1, wherein the contactelectrode comprises a metal.
 3. The MEMS device of claim 1, wherein thecontact electrode comprises silicon.
 4. The MEMS device of claim 1,wherein the contact electrode comprises a conductive coating.
 5. TheMEMS device of claim 1, further comprising a CMOS layer, wherein theactuator electrode and the contact electrode are on the CMOS layer. 6.The MEMS device of claim 1, further comprising a MEMS layer, wherein theactuator electrode and the contact electrode are on the MEMS layer. 7.The MEMS device of claim 1, comprising an anti-stiction coating on thecontact electrode.
 8. The MEMS device of claim 1, further comprising: anintegrated circuit die comprising a transistor; and a MEMS sensorstructure electrically coupled to the integrated circuit die, whereinthe MEMS switch is electrically coupled to the integrated circuit die,wherein the signal is applied to the MEMS sensor structure, and whereinthe MEMS switch is operable to switch the signal.
 9. The MEMS device ofclaim 8, wherein the integrated circuit die comprises a CMOS layer. 10.The MEMS device of claim 8, wherein the signal is characterized by avoltage that is too high to be effectively switched by the transistor.11. The MEMS device of claim 8, wherein the transistor operates in arange of voltages at or below a certain maximum operating voltage, andwherein the signal is characterized by a voltage that is above thecertain maximum voltage of the transistor.
 12. The MEMS device of claim11, wherein the certain maximum operating voltage is a breakdown voltageof the transistor.